An automatic transmission of the type discussed here is known, for example, from DE 199 08 840 A1. This automatic transmission comprises at least one wet-operating disk clutch actuated by at least one hydraulically operated actuator. The actuator comprises a cylinder and a piston guided axially in the cylinder, which enclose a pressure chamber between them. The pressure chamber can be filled with a hydraulic pressure medium, which produces on the piston a closing force that acts in the direction toward the disks of the disk clutch. The hydraulic fluid is delivered to the actuator via an axial bore in a central transmission shaft, which is provided with a radial bore. This radial bore in the transmission shaft is in flow communication with the pressure chamber of the actuator via other radial flow ducts in other transmission components. The feeding of the hydraulic pressure medium thus takes place as usual along the shortest possible path, from radially inside to radially outside.
Since during the operation of the automatic transmission, in addition to the actuation pressure the hydraulic pressure medium filled into the pressure chamber of the actuator is also acted upon by a centrifugal force, automatic transmissions of the type concerned comprise, axially adjacent to the actuator piston, a pressure compensation space in which unpressurized pressure medium also accumulates, and under the action of the centrifugal forces caused by rotation, exerts a force opposing the forces produced by rotation on the pressure medium in the adjacent pressure chamber of the actuator. These forces compensate one another, so that only the desired actuation force acts on the piston as a force differential.
The arrangement of such pressure compensation spaces leads to a previously unavoidable lengthening of the automatic transmission and to an increase of its manufacturing costs.